Concentrated photovoltaic (CPV) systems concentrate sunlight onto photovoltaic surfaces for the purposes of electrical power generation. CPV systems are often mounted on solar trackers to keep the focal point of light on the photovoltaic surfaces as the sun moves across the sky. An early example of a CPV system utilized acrylic Fresnel lenses to focus light on water-cooled silicon solar cells and two axis solar tracking. Other examples of CPV systems utilized hybrid silicone-glass Fresnel lenses and passive heat sinks for solar cell cooling.
Semiconductor properties allow solar cells to operate more efficiently in concentrated light systems, as long as the cell junction temperature is kept sufficiently cool using suitable heat sinks. CPV systems operate most effectively in direct sunlight because diffuse light caused by cloudy conditions typically cannot be efficiently concentrated.
CPV systems offer advantages over conventional flat panel solar cells because CPV solar collectors are typically less expensive than an equivalent area of solar cells. CPV system hardware (solar collector and tracker) is targeted to be priced well under $3/Watt, whereas silicon flat panels are commonly sold at $3-$5/Watt.
Low concentration CPV systems typically have solar concentration levels of 2-100 suns. For economic reasons, conventional or modified silicon solar cells are typically used and, at these concentrations, the heat flux is low enough that the cells typically do not need to be actively cooled. The laws of optics dictate that a solar collector with a low concentration ratio can have a high acceptance angle. Accordingly, low concentration CPV systems typically do not require active solar tracking. Medium concentration CPV systems, which typically have solar concentration levels of 100 to 300 suns, require solar tracking and cooling. High concentration photovoltaic (HCPV) systems employ concentrating optics consisting of dish reflectors or fresnel lenses that concentrate sunlight to intensities of 300 suns or more. The solar cells in these HCPV systems typically require high-capacity heat sinks to prevent thermal destruction and to manage temperature related performance losses. Multijunction solar cells are currently favored over silicon solar cells as they are typically more efficient. Although the cost of multijunction solar cells can be 100× that of comparable silicon cells, the cell cost is typically only a small fraction of an cost of the overall CPV system, which means that system economics can often favor the use of multijunction cells.